The need to create encapsulated magnetic nanoparticles stems not only from the fact that the shell acts to reduce magnetic-induced self-aggregation, but also that the exterior layer can provide a surface amenable to in vivo use and can be conducive to functionalization with molecular recognition moieties (e.g., antibodies, peptides). However, the realization of encapsulated, high magnetic moment magnetic particles is challenging due to the strong interparticle attractive forces that exist during the coating procedure.
Herein is described a method to deposit a uniform coating around a high moment (m˜10−13 emu/particle) core, to provide a particle with a diameter of at least about 100 nm. By depositing multiple polyelectrolyte layers using a layer-by-layer (LbL) process and an exterior coating such as silica, around a magnetic core, a magnetic particle suspension can be stabilized, allowing for the preparation of discrete uniformly-coated individual magnetic particles. The polyelectrolyte layers increase the particle-particle closest approach distance and provide an increased surface charge, which in turn helps minimize magnetic dipole-induced aggregation. These results suggest that successful creation of discrete core-shell magnetic particles is only realized after depositing multiple polyelectrolyte layers. Without the intermediary polyelectrolyte layers, magnetic dipole-dipole and van der Waals interactions lead to the formation of linearly chained magnetic particles embedded in the exterior coating matrix. This encapsulation method can be used to easily and routinely prepare discrete coated magnetic nanoparticles for use in many biomedical applications.